A content distribution system has been widespread in recent years. In the content distribution system, a digital work (hereinafter “content”) such as a movie or music is distributed via a network. For example, a personal computer (hereinafter “PC”) of a user receives content from a content server, and records the content onto an SD memory card or the like purchased by the user.
Since content distributed via a network is digital data having high image quality and high sound quality, copyright protection measures are necessary to prevent distribution of unauthorized copy or the like.
One of copyright protection standards for content is an Advanced Access Content System (AACS). The AACS is a copyright protection standard used in Blu-ray Discs (BD)™
In the AACS, a device key is issued from a key issuing device to a playback device, and a media key block (MKB) is issued from the key issuing device to a content creation device. The content creation device protects content with use of the MKB and a title key that the content creation device itself creates. The MKB, the title key, and the protected content are then recorded onto a BD-ROM to be sold. The playback device removes the protection of the content with use of the device key, the MKB, and the title key, and plays back the content.